The invention described herein relates generally to rotary-drive machining devices and, more particularly, to facedrivers for engaging workpieces along the axes of rotary-drive machining devices.
Many metalworking machines employ rotary-drive devices which support and rotate the workpieces (typically shaft-like pieces) at locations permitting metalworking operations to be performed on the workpieces as they are rotated. Such metalworking machines include lathes, gear-shaping tools, hobbing tools, spline-milling tools and grinding tools. Workpieces are mounted, supported and turned in such machines along a turning axis.
One widely-used device for mounting workpieces is known as the facedriver. Facedrivers engage one end of a workpiece while the opposite end is engaged by a tailstock. The term xe2x80x9cfacedriverxe2x80x9d is used because such device applies force to the end of the workpiece, thereby permitting metalworking operations to be performed along the entire axial length of the workpiece in a single operation. The facedriver is a preferred workpiece-mounting device for rotary-drive machining apparatus because it contacts and applies forces to only the end face of a workpiece.
Each facedriver typically includes a base member (or xe2x80x9cdriving headxe2x80x9d) with a forward end, an axially-aligned, forwardly-spring-biased centerpoint member slidably disposed in the base member, and drivepins slidably disposed in the base member around the centerpoint member and supported rearwardly by some sort of means to cause some interactive adjustment of the drivepins as they engage the workpiece. The centerpoint member is a male member with a pointed distal end for engaging a female opening at the end of the workpiece, and serves the purpose of providing axial support for the workpiece throughout the machining operations. The drivepins have distal ends engaging the workpiece and imparting to the workpiece the turning motion of the facedriver as it rotates. The drivepins are adjustably held in drivepin holes in the carrier body and are supported rearwardly (at their proximal ends) in various ways.
The two most widely used commercially-available facedrivers have two principal types of structures for rearward support of drivepins. One involves the pins bearing on a wobble ring and the other involves the pins bearing on a hydraulic fluidxe2x80x94an oil reservoir. These rearward support means permit the drivepins to adjust in different ways to irregular face variations of the workpiece endxe2x80x94such as end surfaces which are off-normal (i.e., non-perpendicular) with respect to the axis of the workpiece or concave, or which have various other irregular or erroneous configurations. Each of the two principal types of face-driver structures, however, has significant disadvantages and/or shortcomings.
In facedrivers with wobble rings, the wobble ring is able to move so that axial movement of one or two of the drivepins in one direction on one side of the centerpoint member causes compensating opposite axial movement of some of the drivepins on the opposite side of the centerpoint member. However, because of the rigid connections, less than all of the drivepins (e.g., only three of the drivepins) will make fully-solid contact with the workpiece at any one time unless there is an absolute true perpendicular mounting.
While this type of facedriver has imperfect workpiece engagement by the drivepins, it does provide relatively good workpiece engagement by the centerpoint member. More specifically, an advantage of wobble-ring structures is that rearward movement of the wobble ring caused by drivepins applies rearward force on a cone or a sleeve which in turn causes collapse of a collet, thereby gripping the centerpoint member and enhancing the axial force with which it engages the workpiece. This action gives stronger workpiece support for better on-axis stability when trans-axial tool pressure is applied on the workpiece in various metal-working operations. That is, the workpiece is supported fairly well against side-to-side shifting. As indicated, however, the problem of facedrivers with wobble-ring support for their drivepins is a lack of solid engagement of all drivepins with the workpiecesxe2x80x94because of irregular or imperfect workpiece ends as described above.
Different advantages and disadvantages exist for facedrivers of the type in which the drivepins are supported on an oil reservoir. Given the non-compressibility of oil, the oil serves to provide compensation for each of the pins and gives you a true equalizing adjustment. The drivepins are supported on a single reservoir the shape of which accommodates the drivepin array. This hydraulic support tends to provide excellent workpiece engagement for all of the drivepins, regardless of the irregularities or imperfections of workpiece ends. All pins engage varying workpieces with equal pressure, regardless of the axial positions of any of the pins, because they are suspended on a common reservoir.
However, a significant disadvantage and shortcoming of such oil-reservoir facedrivers is that the drivepins are required to serve too much of a role in holding workpieces in proper axial alignment. While it is supposed to be the role of the centerpoint member to insure proper axial alignment during operations, when the workpiece is loaded against the drivepins (against the resistance of the tail stock engaging the other end of the workpiece), the force with which the drivepins engage the workpiece exceeds the force by which the centerpoint member engages the workpiece.
The result is that there is a tendency for the centerpoint member to float because the only thing that helps it apply force to the workpiece is a spring behind it. The problem is that because the spring pressure does not equal the hydraulic pressure, the drivepins end up both driving and more or less suspending the workpiece. This is potentially problematic, particularly when substantial radial loads are applied to the workpiece during machining operations.
In summary, there is a need for an improved facedriver which overcomes each of the differing problems in prior art devices.
It is an object of this invention to provide a facedriver overcoming the problems and shortcomings of the prior art, including those noted above.
Another object of this invention is to provide an improved facedriver which exhibits even and consistent engagement of the drivepins with the workpiece, without any sacrifice in the workpiece-centering and workpiece-holding functions of the centerpoint member.
Another object is to provide an improved facedriver which provides enhanced workpiece-engagement under increased loading conditions without any sacrifice in the ability of drivepins to conform to the workpiece-end irregularities.
Still another object of the invention is to provide an improved facedriver with balanced drivepin engagement with workpiece ends despite workpiece-end variations and commensurately enhanced centerpoint member loading force as drivepin forces increase.
It is a further object of this invention to provide an improved facedriver with excellent workpiece engagement and holding properties and simple construction and operation.
These and other objects of the invention will be apparent from the following descriptions and from the drawings.
This invention is an improved facedriver which overcomes significant problems in the industry, including those described above. The facedriver of this invention is an improvement in facedrivers of the type including a base member with a forward end, an axially-aligned, forwardly-biased centerpoint member slidably disposed in the base member, and drivepins slidably disposed in the base member around the centerpoint member and supported rearwardly by hydraulic fluid in drivepin portions of a fluid-containing chamber within the base member.
The facedriver of this invention includes a grip member within the base member and contacting the lateral surface of the centerpoint member to apply radial gripping force thereon to enhance the axial loading force applied by centerpoint member to the workpiece under certain conditions. The fluid chamber, in addition to its drivepin portions, includes a grip portion adjacent to the grip member for fluid contact therewith. Thus, loading forces applied through the drivepins are transmitted to the grip portion of the fluid chamber, so that such fluid pressure results in application of radial force on the lateral surface of the centerpoint member through the grip member.
The grip portion of the fluid chamber and the grip member are configured and arranged such that varying hydraulic fluid pressure in the fluid chamber, caused by forces transmitted to the fluid by the drivepins, result in varying loading forces being applied by the centerpoint member on the workpiece. More specifically, the grip member, the drivepins, and the grip portion and drivepin portions of the fluid chamber are configured and arranged, and the biasing of the centerpoint member selected, such that the force of the drivepins applied to the workpiece upon facedriver loading and the resulting increased fluid pressure in the fluid chamber serve to cause the centerpoint member to apply force to the workpiece upon facedriver loading which approaches the force applied by the drivepins.
In highly preferred embodiments of this invention, the grip member, at the grip portion of the fluid chamber, has a radially-compressible portion bearing on the lateral surface of the centerpoint member. The radially-compressible portion is preferably in the form of a sleeve, and such sleeve is preferably of metal. It is most preferred that the radially-compressible sleeve be integrally formed with the remainder of the grip member. It is highly preferred that the grip member be sleeved over the centerpoint member and that the grip portion of the fluid chamber be formed in part by an annular void along the radially-compressible portion of the grip member.
In such embodiments, it is highly preferred that the fluid chamber includes at least one connecting portion extending from the annular void to the drivepin portions of the fluid chamber. Such connecting portion preferably extends rearwardly along the grip member from the annular void to the drivepin portions of the fluid chamber.
Preferred embodiments are now described in more detail. The base member of the facedriver of this invention preferably forms various voids and spaces in it for the movable components and to accommodate the functions involving hydraulic fluid. More specifically, the base member forms a center void along the axis, drivepin voids around the axis, and a fluid chamber around the axis which includes a grip portion and drivepin portions adjacent to the drivepin voids. The forwardly-biased centerpoint member has a lateral surface and extends axially along the center void within the base member to a centerpoint-member distal end beyond the forward end of the base member. The drivepins are in the drivepin voids and extend forwardly to drivepin distal ends and rearwardly to drivepin proximal ends which are adjacent to the drivepin portions of the fluid chamber for support on the hydraulic fluid. The grip member in the center void has an inner surface against which the centerpoint member is slidably engaged and an outer surface with a mid-portion adjacent to the grip portion of the fluid chamber for fluid contact. As already noted, the grip portion of the fluid chamber and the grip member are configured and arranged such that varying hydraulic pressure in the fluid chamber applies varying radial gripping force on the centerpoint member through the grip member.
In certain preferred embodiments, the center void in the base member includes a forward portion with a cylindrical wall of first diameter, a middle portion with a cylindrical wall of second diameter greater than the first diameter, an a rearward portion with a cylindrical wall of third diameter greater than the second diameter. That portion of the grip-member outer surface which is forward of the radially-compressible portion of the grip member engages the cylindrical wall of first diameter, and one or more connecting portions of the fluid chamber are along the cylindrical wall of second diameter.
The grip member preferably includes a forward cylindrical bore defined by the grip-member inner surface and a rearward axial recess abutting the cylindrical bore. In such preferred embodiments, the rearward axial recess receives a spring, typically a coil spring, which bears on the centerpoint member to provide its forward bias. In such preferred embodiments, the spring is selected such that its axial force, along with the resistance forces in the centerpoint member generated hydraulically due to the particular configuration and arrangement of parts causes the centerpoint member to apply force to a workpiece which approaches the force applied by the drivepins.
In a broad form, this invention is an apparatus for applying force on an object which includes: a base member with a forward end; a forwardly-biased first slidable member slidably disposed in the base member along an axis; one or more additional slidable members each of which is slidably disposed in the base member in a generally axially-parallel position and supported rearwardly by hydraulic fluid in a chamber within the base member; a grip member within the base member and contacting the first slidable member; and a grip portion of the fluid chamber, such grip portion being adjacent to the grip member for fluid contact therewith such that varying fluid pressure in the fluid chamber applies varying gripping force (e.g., radial gripping force) on the first sidable member through the grip member.